While the multi-segment metering systems built into today’s D-SLR cameras provide excellent exposures in an amazingly wide range of situations, there are some scenes that can fool them. Learning to recognize and compensate for those situations will make you a better photographer.
One situation that drove me crazy until the simple solution hit me was sunlit water birds swimming across bright and dark reflections in a local lake. When the bird swam across a bright area (reflecting the bright sky), the meter would reduce exposure due to the brightness, and I’d get an underexposed bird. Conversely, when the bird swam across a dark area (reflecting shaded foliage), the meter would increase exposure, and I’d get an overexposed bird. It’s easy enough to compensate for one situation or the other, but with the birds swimming from bright to dark to bright to dark, it’s just too much bother‚ if not impossible‚ to determine and adjust the proper amount of exposure compensation continuously as I track the bird.
The simple solution turned out to be the old Basic Daylight Exposure (BDE, for short): For a subject lit by direct frontal sunlight, the correct exposure is a shutter speed of 1/ISO at ƒ/16 or equivalent: at ISO 200, the exposure would be 1/200 sec. at ƒ/16 (since I work handheld and like faster shutter speeds, I’d use 1/800 sec. at ƒ/8). Switch to manual exposure mode, set the BDE, and it doesn’t matter what kind of reflections the sunlit bird swims across. As long as the bird remains sunlit, it will be correctly exposed‚ no need to reset anything as you shoot.
Of course, this assumes the subject stays in direct sun. If it swims from a sunlit area to a shaded one or if a cloud passes across the sun, the bird will be underexposed. This is easily avoided by setting up where the subjects are always in direct sun (and picking a cloudless day!). If I can’t do that, I’ll switch back to aperture-priority AE mode and shoot only when the subject is against a bright background or against a dark one, setting exposure compensation accordingly. When shooting very early or late in the day when the sun isn’t as bright, you’ll have to give more exposure than the BDE. Set the exposure you think is right, then check it on the LCD monitor (or better still, use the histogram on the LCD monitor). Remember that the light level changes rapidly when the sun is near the horizon, so this might be a time to go back to AE.
One more caveat: I’ve found that my D-SLRs blow out white birds at the BDE. So when photographing egrets or gulls in direct sun, I reduce exposure one stop from the BDE (for example, I use 1/1600 sec. at ƒ/8 for ISO 100). Your D-SLR might require more or less compensation for white subjects; it’s always a good idea to do some testing with your own camera to see how it handles various exposure situations.
This trick comes in handy for perched birds, too, when moving the camera a bit to one side or the other for that perfect angle changes the background from bright sky to dark foliage, as well as for flying birds passing areas of bright sky and dark foliage. Determine the proper exposure for the sunlit subject, lock that in with manual exposure mode, and bright or dark backgrounds can’t fool the meter because you’re not using it.